1. Field of the Invention
The subject invention relates generally to vibration damping of suspension and steering systems in a motor vehicle. More specifically, the subject invention relates to vibration damping using a flexible drive plate in a rotary type damper.
2. Description of the Prior Art
Rotary dampers have been installed in both steering and suspension assemblies of motor vehicles to dampen the amount of vibration detected by the vehicle operator from such variables as vehicle speed, road bumps, wheel alignment, wheel chatter, and tread wear. Rotary dampers of this type reduce the amount of vibration transferred to the vehicle operator by resisting rotational velocity generated from a pinion associated with either the steering assembly or the suspension assembly. The rotational velocity is resisted by torque generated by the rotary damper thereby reducing the vibration transfer to the driver. The torque is derived from a clutch-like sheer resistance generated by a fluid, generally Newtonian, when a rotor disposed within a vibration damper assembly and operatively connected to the pinion receives rotational velocity from the pinion.
The rotational velocity generated by the pinion connected to the rotary damper varies with the amount of vibration absorbed from the operating variables. A variable level of torque is required to provide uniform damping at both high rotational velocities and at low rotational velocities.
A typical rotary damper assembly that utilizes Magneto-Rheological (MR) fluids includes a core disposed within a housing. The core is operatively connected to a rotational velocity-generating member, such as a pinion, that is connected to a steering or suspension assembly. A conductive sleeve is positioned between the housing and the core. A coil is positioned adjacent the sleeve and is capable of generating a magnetic field that is transmitted through the sleeve. An annular plate separates the core from the sleeve and defines a viscous chamber and a Magneto-Rheological fluid chamber. The viscous chamber is disposed between the sleeve and the housing and the MR chamber is disposed between the sleeve and the core. A viscous fluid is contained within the viscous chamber and MR fluid is contained within the MR chamber. The viscous fluid behaves as a Newtonian fluid throughout operation of the assembly. The MR fluid behaves as a Bingham plastic when it is subjected to the magnetic field and, otherwise, behaves as a Newtonian fluid.
The steering damper provides the ability to vary the amount of torque generated by the vibration damper assembly. When not subjected to the magnetic field, the torque is generated by the Newtonian fluid, which is preferable at low velocity. When subjected to the magnetic field, the MR fluid is transformed from a Newtonian fluid to a Bingham plastic, which generates a torque that is preferable at higher velocities.
Although this type of damper design has proven to be reliable, binding can occur when the rotor is pulled out of alignment with the core by the end of the pinion shaft as a result of misalignment due to production and dimensional tolerances. This misalignment, also known to those of skill in the art as runout, is a problem inherently due to dimensional tolerance conditions that allow axial misalignment. Also, any looseness or lash in the spline coupling between the pinion shaft and the rotor allows vibration to bypass the damper undamped. This looseness is due to necessary build clearances in the spline dimensions and normal wear.
The subject invention provides a steering damper assembly comprising a rotor sleeve having a first end adapted to be mounted to a pinion shaft. A drive plate is disposed on the open first end of the rotor sleeve. A core is co-axially disposed in the rotor sleeve and closes the open second end defining a magnetic fluid chamber between the core and the rotor sleeve. A Magneto-Rheological (MR) fluid is injected into the MR fluid chamber. The MR fluid includes a variable shear force when subjected to a magnetic field to provide a torque resistance to the rotational velocity derived from the pinion.
The drive plate is flexible and securely attached to the open first end of the rotor sleeve. The pinion is inserted through the drive plate and is secured by a nut. The drive plate receives flexibility from a plurality of drive plate holes disposed in the surface. The flexibility in the drive plate increases the manufacturing tolerance of the assembly. Therefore, if the pinion is not properly aligned with the core when being mated to the assembly, the drive plate will flex to provide a broader access to the core. Further, if the pinion is received by the core in a non-aligned orientation, the drive plate will remain in a flexed state to provide the necessary access to the core. Therefore, the damping properties of the assembly will not be reduced if the final alignment of the pinion with the core is not precise due to manufacturing variability. Clamping the drive plate to the pinion shaft with a nut provides an initial alignment and a lash free connection not provided by a splined connection.
A further advantage of the apertures bored through the flexible drive plate is the ability to inject damping fluid through the apertures into the steering damper assembly during the manufacturing process. Thus, the complexity and difficulty of manufacturing the steering damper is reduced with the addition of the apertures in the drive plate.